The choice of Sarah Palin as John McCain’s running mate has all sorts of interesting political implications, which are being diced and parsed as I write. But I’m more interested in the long-term cultural implications of the choice of Palin, whether the McCain–Palin ticket wins or loses in November, for one of the most vexing horizons of impossibility in our culture: the abortion rate among unborn babies diagnosed with Down Syndrome.

Upwards of 85 percent of parents who receive a prenatal diagnosis of Down Syndrome elect to terminate the pregnancy, according to several studies in the peer-reviewed journal Prenatal Diagnosis. A 1999 British study in that journal found the termination rate to be between 91 and 93 percent. When I was a teenager in the 1980s, I remember seeing many people my age and younger who had the distinctive facial and behavioral characteristics of Down children. These days I rarely see a Down Syndrome child at all.

What is peculiar about Down Syndrome as a reason for termination is that, plainly put, you rarely meet a Down Syndrome “sufferer” who is notably unhappy. The condition has a range of manifestations, some more disabling than others, but many, many persons with Down Syndrome thrive as children and adults, even if they may not have the same range of capabilities as you or I do.

The fact that this syndrome has become a reason for termination is evidence of the terrible power of culture. A culturally neutral artifact (prenatal diagnosis of congenital diseases) combined with a culturally tragic artifact (elective abortion) begins to make it plausible that parents should avoid the challenges and risks of a Down pregnancy by ending it. The decreasing number of children born with the condition begins to make it more difficult to imagine that “normal” families can absorb the stresses of raising such a child, and undermines public support for public programs that support families who have made that decision. Which, over time, makes carrying a Down Syndrome baby to term ever more inconceivable, leading to increased rates of termination, leading to decreasing plausibility . . . until one day the burden of bringing a Down Syndrome child into the world is seen as so grave that less than 10 percent of parents take the risk.

But Sarah and Todd Palin have done it. I cannot think of any other public figures in my adult life, at least of the prominence they are about to enjoy or endure, who have made this decision. They will cause many, many families to reconsider the horizons of the possible. Their public example could very well lead to a cultural sea change—a dramatic shift in the “horizons of the possible.” That phrase from my book is no metaphor. Those horizons are so real that, for a future generation of children and their parents, they are quite literally a matter of life and death. For this reason, which utterly transcends politics and this year’s election, the sudden prominence of the Palins is, in the deepest sense, an extraordinary act of public service.